Run up and get the silver key. As soon as your character is moving to the tile with the silver key, immediately run to the right two spaces, down two spaces and up one space. Wait for a series of fast explosions to pass. After which, there will be 5 explosions with a short delay between each of them. As soon as the 5th explosion has happened, taking care not to get blown up, you can run up one, right two and up two, before explosion 13, after which a two more explosions will occur and a bomb will appear in the column where you first were. Now that it's safe, get the last two crystals.